Progesterone is a hormone your ovary makes after you ovulate (release an egg). The part of the ovary that released the egg turns into a small, temporary gland, and its main job is to make progesterone. This gets the lining of the womb ready, after estrogen has built it up.¹

Its most important job is to balance estrogen. Estrogen makes the lining of the womb grow. Progesterone stops it growing and changes it into a calm, stable layer.² When progesterone falls at the end of the month, the whole lining sheds as your period, and the next cycle starts fresh. This is why the lining does not keep building up month after month.³

Progesterone also acts in the brain. Your body turns part of it into a substance called allopregnanolone, which has a calming effect. This is why progesterone taken by mouth can make you slightly sleepy, and why it is taken at night.^4,5

Most women who come to us are at the age when these hormones change the most.

• The early transition. Fewer eggs are left, so fewer cycles release an egg. A month without an egg is a month without progesterone. Progesterone therefore falls first, often from about 5 years before the last period, while estrogen still swings up and down, and in some months is even higher than when you were younger.⁶
• The late transition. Periods start to skip for more than 60 days at a time, and estrogen becomes clearly low. Hot flushes and vaginal dryness become much more common.^6,7
• After menopause. Menopause means no period for 12 months, at an average age of 52. The ovaries stop making both estrogen and progesterone, and progesterone falls to almost zero.^6,8
• Surgery to remove both ovaries. Hormones stop all at once, so symptoms are usually stronger than in a natural menopause.⁴

• Reproductive years: Periods: Regular; Estrogen: Rises and falls with each cycle; Progesterone: Made every cycle after ovulation
• Early transition: Periods: Cycle length changes; Estrogen: Swings, some months high; Progesterone: Missing in cycles without ovulation
• Late transition: Periods: No period for more than 60 days; Estrogen: Mostly low; Progesterone: Very little
• After menopause: Periods: None for 12 months; Estrogen: Low (a weaker form, estrone, takes over); Progesterone: Almost zero

The pattern of a woman’s hormones from the reproductive years to after menopause. This is an illustration, not real values.^6,7

When your doctor asks whether your periods are regular, these are the rules we use:

• Age 45 and over. Your periods count as changing when your cycle is 7 days or more longer or shorter than your usual cycle, again and again. A gap of more than 60 days without a period means the late transition, and 12 months without a period means menopause.⁷
• Under 45. Most normal cycles last 25–30 days. Periods count as irregular when a cycle is shorter than 21 days, longer than 35 days, or you have fewer than 8 periods a year.^1,9
• Heavy bleeding means flooding, or passing clots.¹⁰
• Menopause means no period for 12 months in a row. If you take something that can stop periods by itself, such as progesterone every night or a hormonal coil, a missing period may come from the medicine, so we cannot count the 12 months in the usual way.⁷

This is why we ask about the first day of your last period and how long your cycles are. It helps us time your blood test and read your bleeding pattern. If you are not sure, that is fine. We will find the best way to read your results.

• You are in your 40s and your cycles are starting to change. Months without ovulation become more common, so progesterone falls before estrogen does.⁶
• You are past menopause.⁶
• Your ovaries were removed by surgery.⁴
• You use estrogen treatment and still have your womb. You need progesterone to protect the lining, whatever your own level.⁷

There is no standard checklist for “low progesterone”. Medical guidelines describe changes in the years before menopause, such as irregular or heavy periods and hot flushes.⁷ Physicians who focus on optimal hormone levels explain that many signs of low progesterone are really signs of estrogen that is no longer balanced:

• Mood: feeling tense, irritable or anxious, especially before your period, and poor sleep when you feel tense
• Body: swollen or tender breasts before your period, bloating, a puffy face, swollen feet and ankles
• Periods: heavy or painful periods, and deep pain during sex
• Timing: symptoms that start or get worse 1–3 weeks before a period

These signs have many other causes. Your doctor looks at the whole picture with you.

This is what research has found. “Clinical trials” means the result comes from randomised trials. “Early research” means smaller or observational studies. The best-proven benefit of progesterone is protecting the womb lining when you use estrogen; this is explained on our estrogen page.

• Hot flushes and night sweats after menopause (clinical trials). In 133 women 1–10 years after menopause, progesterone alone every night for 12 weeks reduced hot flushes and night sweats more than a dummy treatment, at a higher dose than we use.¹¹ Menopause societies accept this result, but note that it is outside the licensed uses and there is no long-term data yet.^4,12
• Night sweats and sleep in the years around menopause (clinical trials, secondary results). In 189 women aged 35–58 taking progesterone alone, the main hot-flush score did not differ from a dummy treatment, but night sweats fell and sleep quality improved, also at a higher dose. The researchers noted the study was too small to be sure.^13,14
• Falling asleep (early research). After menopause, progesterone helped women fall asleep faster, but did not make them sleep longer in total.⁷ A small study of 8 women found it helped on nights when sleep was disturbed.¹⁵
• Mood (clinical trials, with estrogen). An estrogen patch with progesterone cut new, clinically significant depressive symptoms from 32.3% to 17.3% over 12 months, only in the early years of the transition. Progesterone was given on a different schedule from ours.¹⁶
• Blood clots and cholesterol (early research). With estrogen applied to the skin, progesterone was not linked to a higher risk of blood clots, unlike some synthetic progestins.⁷ It also does not cancel estrogen’s good effect on HDL (“good”) cholesterol.¹⁷
• Bones before menopause (early research). Cycles that release no egg have been linked with bone loss, and low progesterone may add to faster bone loss in the years before menopause.¹⁸

Clinical trials so far have not shown that progesterone helps bone strength after menopause,¹⁸ total sleep time⁷ or memory and thinking.¹⁹

“Progestogen” is a word for anything that acts like progesterone. There are two kinds. Micronized progesterone is the same molecule your ovaries make. Progestins are man-made versions with a changed structure.⁴ Most research and most news stories about “hormones and cancer” are about progestins, so the results cannot simply be applied to progesterone.

• Structure: Micronized progesterone (what we use): Exactly the same as your own progesterone⁴; Synthetic progestins: Chemically changed⁴
• Sleep: Micronized progesterone (what we use): Turns into allopregnanolone, which helps sleep⁵; Synthetic progestins: Does not
• Breast: Micronized progesterone (what we use): Data are mixed; the risk looks lower (see below); Synthetic progestins: Clearly raises risk when used with estrogen⁷
• Blood clots, with estrogen on the skin: Micronized progesterone (what we use): No increase⁷; Synthetic progestins: Some types increase the risk⁷

We want you to have the full picture, not just the headlines.

• Most of the extra breast cancer risk comes from synthetic progestins. In the large WHI trial, which used a synthetic progestin with estrogen, breast cancer rose by 9 cases per 10,000 women each year.^4,20 An international review concluded that most of the extra breast cancer risk from hormone therapy comes from synthetic progestins.⁷
• Body-identical progesterone looks safer for the breast, but the data are mixed. In a large French study (E3N), estrogen with progesterone carried no higher breast cancer risk than no hormones.²¹ A combined analysis found the risk was about one-third lower than with progestins, although the evidence quality was low.¹⁷ Another very large analysis did not find a clear difference by type.⁸
• Progesterone on its own has not been studied for long-term cancer safety. Its known action is to calm the lining, and there is no evidence that it raises risk.^4,12

Cancer becomes more common with age, with or without hormones. The age when women start hormones is also the age when these cancers naturally become more common. So a cancer found while using hormones is not always caused by hormones, and age-based screening is still needed for everyone.

New cases per 100,000 women each year (age group: rate)

• Breast: age 40–44 75.5 (62.0) · 50–54 126.4 (96.0) · 55–59 143.3 (111.7) · 65–69 174.7 (106.1) · 75+ 190.8 (60.0)
• Cervix: age 40–44 23.1 (21.9) · 50–54 36.3 (28.1) · 55–59 38.5 (29.8) · 65–69 36.2 (30.3) · 75+ 27.8 (24.6)
• Womb lining: age 40–44 6.5 (6.3) · 50–54 22.6 (18.0) · 55–59 31.0 (29.0) · 65–69 42.5 (29.1) · 75+ 37.8 (10.9)
• Ovary: age 40–44 8.6 (7.9) · 50–54 16.9 (15.5) · 55–59 19.9 (18.3) · 65–69 24.6 (17.5) · 75+ 25.7 (12.5)

The first number is for women worldwide; the number in brackets is for women in Thailand.^22,23 For example, among 100,000 women aged 55–59 worldwide, about 31 develop womb-lining cancer each year, up from about 7 at age 40–44, without any link to hormones. Breast cancer is the most common cancer in Thai women.²⁴

Putting the risk in proportion. A number like “3 times higher” sounds frightening, but it depends on how common the cancer is to start with. In Western women of average weight who never used hormones, the chance of breast cancer between ages 50 and 69 is 6.3%. With 5 years of estrogen plus a daily progestogen it is 8.3%.⁸ The extra breast cancer risk from hormone therapy is small, and the same as or lower than the extra risk from too little exercise, obesity or drinking alcohol.⁷

• Progesterone blood test. We use it to support our decision, not as a target. Guidelines do not recommend using hormone levels to set the dose,⁷ so your symptoms guide us most. If your periods are regular, the best day is about 7 days before your next period (day 21 of a 28-day cycle), because progesterone is highest about a week after ovulation. If your periods are irregular, we use the date your period-tracking app predicts. After menopause you do not need this test, because the level is very low in everyone.^1,6
• Vaginal ultrasound before you start. Everyone with a womb has a vaginal ultrasound with a gynaecologist before starting. A result from the past 12 months is fine. If you still have periods, book it just after your period ends, because the lining changes through the month. Safety comes first for us. From your 40s the risk of cancers of the womb and ovaries starts to rise, and we want to be sure your risk is as low as possible before you use hormones. We do not start treatment without this result. It also gives us a starting point, so we can look after bleeding in the first months calmly in our clinic.
• A yearly gynaecology check. Every woman using our hormones sees a gynaecologist before starting and once a year after that, for an internal examination and cervical screening.²⁵
• A mammogram if you also use estrogen. If you are 45 or older and use estrogen with us, we need a mammogram result before you start estrogen, and once a year while you use it. This is because the data on breast cancer risk come from progesterone used with estrogen.
• A pregnancy test. We offer it to everyone who still has periods, because the label says to stop progesterone straight away in pregnancy.² If you do not use contraception, we test before you start, and again whenever a period is missed or your bleeding pattern changes.

Progesterone is suitable for most women, but it is not one size fits all.

Some women need special consideration before starting. This does not mean you can never use it. It means we need to look at your situation first, or that another doctor should be in charge of this part of your care. Our doctor checks whether any of these apply to you:

• An allergy to sunflower seeds. The capsules contain sunflower oil, so we do not start them.²⁶
• Breast, womb-lining, ovarian or other hormone-sensitive cancer, now or in the past. We refer you back to your specialist.²
• Vaginal bleeding that has not been explained. A gynaecologist needs to find the cause first.^2,7
• Pregnancy or breastfeeding. We do not start, because the label says to stop if you become pregnant, and progesterone passes into breast milk.² If you would like to become pregnant, a gynaecologist is the right doctor to plan this with you.
• A blood clot in a vein, now or in the past. For a past clot that has healed, we can still give our hormones. Guidelines consider estrogen on the skin with body-identical progesterone a safe choice, and this combination did not raise the risk of clots, so we explain to you why the product label is more cautious.^7,2 For a clot you have now, we do not start estrogen. Progesterone on its own is decided together with the specialist treating the clot.^2,7
• A past stroke, heart attack or chest pain from the heart, however long ago. We do not start, and we advise you to see a specialist. Hormones in this situation need a specialist involved in your care, which a wellness clinic is not set up to provide.^2,7
• Abnormal thickening of the womb lining that has not been treated, uncontrolled high blood pressure, acute liver disease or liver tests that have not returned to normal, or porphyria (a rare blood condition). We do not start; a specialist treats these first.^2,7

Some women we refer rather than treat. We tell you this now so you do not lose time.

• Under 40, including premenstrual syndrome (PMS). Treating PMS is not the aim of our hormone service, and PMS has treatments with better evidence, which a gynaecologist provides.²⁷
• Age 40–44 with irregular periods, early menopause before 45, or surgery to remove the ovaries before 45. The cause needs to be found first, for example PCOS, thyroid problems or a hormone called prolactin. A gynaecologist who follows you over time is the right person to care for you.
• PCOS. PCOS is a lifelong condition that affects much more than periods: blood sugar, the heart, skin and hair, sleep, mood and fertility. It needs a long-term plan, and its main treatments are outside our clinic.⁹ Our medicine can protect the womb lining, but cannot cover the rest.
• Age 60 or over and starting hormones for the first time. This is not because you should not have hormones. It is because they should be started by a doctor who can look for causes and check for cancer directly, at an age when these cancers are more common. If you already use our hormones when you turn 60, you can continue with us, and we review the benefits and risks with you every year.

We give progesterone for two reasons: to ease symptoms of low progesterone from age 40, and to balance estrogen if you also use estrogen. Your doctor sets your dose and adjusts it by how you feel.

• On its own: we start low and increase only if your symptoms have not improved enough. Progesterone can make you sleepy, so we look for the lowest amount that works.
• With estrogen, if you have a womb: you take the full protective amount from the first night, on the same day you start estrogen, to protect the womb lining. Why this protection matters is explained on our estrogen page.
• With estrogen, after a hysterectomy: there is no lining to protect. We give progesterone to balance estrogen and to help symptoms such as sleep. Standard guidelines give estrogen alone in this situation, so your doctor will explain this choice with you.

Why every night, even if you still have periods. You may have heard of taking progesterone on only some days of each month. Guidelines often use that method for women who still have periods,⁷ but we chose every night for everyone, for three reasons:

1. Counting days is easy to get wrong. Taking it on the wrong days, or not regularly, is a main cause of both breakthrough bleeding and poor protection of the lining.^7,10 Every night means there is nothing to count.
2. Taking it on some days of the month for more than 5 years raises the risk of womb-lining cancer almost 3 times.^7,28 Taking it every night, once bleeding has settled, carries an even lower risk than using no hormones at all.⁷
3. Physicians who focus on optimal hormone levels also give it every night, and find that benefits such as sleep are steadier.

There are two trade-offs. If you still have periods, bleeding can be irregular (see below). And daily use is linked with slightly more breast cancer than monthly courses: in women who start at 50 and use hormones for 5 years, about one extra breast cancer for every 50 users with daily use, compared with one extra for every 70 users with monthly courses. This data comes mostly from synthetic progestins, not body-identical progesterone.^8,7

Contraception. Progesterone is not a contraceptive. You can still become pregnant until menopause, and pregnancy at this age carries more risk.^2,7 If you become pregnant, all our hormones must stop. This is not because they harm the baby: in many pregnancies exposed to progesterone, no harm to the baby has been found.² Your doctor will talk with you about contraception that works with our hormones. We do not use the combined pill with our hormones, because it already contains estrogen, and its risk of blood clots rises from about age 40.²⁹

If you are past menopause, your body no longer makes its own estrogen. Your hormones come only from treatment and stay steady, so the lining becomes thin and calm. If you use estrogen with progesterone, bleeding may happen in the first months and usually stops within 6 months.¹⁰ If you take progesterone on its own after menopause, any bleeding is different: please stop the capsules and tell us, and we will refer you to a gynaecologist. Without estrogen treatment there is no expected reason for bleeding, and bleeding after menopause needs checking.^7,4

If you still have periods, the capsule does not switch off your ovaries.¹⁰ You then have two sources of hormones: the capsule, which is steady every day, and your ovaries, which go up and down by themselves. This can cause three kinds of bleeding:

• Your own periods may continue. In months when you still ovulate, your own progesterone falls at the end of the cycle and you have a period, much like before.
• Your ovaries release a burst of estrogen. The steady progesterone may not fully balance it. Parts of the lining grow faster than their support, new tiny blood vessels are fragile, and you get spotting on days you cannot predict.³⁰
• The lining becomes very thin. Thin lining has less stable blood vessels, so light spotting can happen by itself. This is usually light and does not mean anything is wrong.³⁰

Over time, bleeding usually becomes less. Something similar is seen with the hormonal coil: irregular bleeding is common in the first 6 months, but by 6 months 44% of women have no periods at all.³⁰ As long as your ovaries still work, some bleeding can come and go until your periods stop completely.

Why bleeding can be irregular if you still have periods and take progesterone every night. This is an illustration, not real values.^7,10,30

When your ultrasound before starting was normal, spotting in the first 6 months after starting, or the first 3 months after a dose change, is common and not a cause for alarm. Please tell us about it. We look after your safety and decide whether anything needs to be done.

Why we may adjust your medicine when you tell us about spotting. Breakthrough bleeding means bleeding outside the pattern expected from your medicine. It is most common in the first 6 months, and in women using estrogen with daily progesterone it can affect up to 41%.⁷ Guidelines say the amount of progesterone must match the amount of estrogen.^7,10 When there is not quite enough, part of the lining keeps growing and becomes fragile. In a study of women using estrogen, progesterone every day at the higher dose kept the lining calm in 100%, compared with 56.4% at a lower dose taken on most days.¹⁰ So before anything else, we check that you take it every night, because missed doses are a common cause.^7,10 Then we may adjust your medicine. If you take progesterone on its own, we may raise the dose. If you take estrogen too, we may lower the estrogen instead.^7,10 If bleeding still continues, a hormonal coil is the next option.⁷

Why a higher progesterone dose can reduce breakthrough bleeding. This is an illustration, not real values.^30,10

When we arrange an ultrasound. We refer you to a gynaecologist for a vaginal ultrasound if:

• you are past menopause and take progesterone on its own, and have any bleeding. In this case you stop the capsules until you have been checked;
• bleeding is heavy (flooding or clots), or happens almost every day for more than 4 weeks, even if light;¹⁰
• you use estrogen and bleed for a third time after we have adjusted your medicine;
• you have risk factors for womb-lining cancer (we go through these with you before you start; they are listed on our estrogen page) and the bleeding is heavy (flooding) or like a period;
• after the first 6 months (or 3 months after a dose change), bleeding has not settled after 6 months of adjusting your medicine, comes back after it had stopped, or lasts more than 7 days.¹⁰

Bleeding after sex is different: we refer you to a gynaecologist to check the cervix (neck of the womb), because the cause is usually there rather than in the lining.¹⁰ If you use the progestin-only pill and bleed often, we first change your contraception, because that pill often causes irregular bleeding by itself.

When we refer you, please book the check within the month. There is no need to panic: changes in the lining develop slowly, over years. While you wait, you can keep using your hormones, unless we have asked you to stop, because continuing does not affect the test results.¹⁰ If you have sudden, very heavy bleeding, go to a hospital straight away.

• Before you start: your health history, blood tests, the vaginal ultrasound and a gynaecology check, and a symptom questionnaire.
• Follow-up visits: 3 months after you start or change your dose, then every 6 months once things are stable.
• At every visit we repeat the symptom questionnaire, look at your bleeding record, check that you take your capsule every night, ask about your yearly gynaecology check and, if you still have periods, your contraception.
• Once a year we review the benefits and risks of your treatment with you.

Please log every day of bleeding in a period-tracking app (we suggest Flo, but any app or a calendar is fine) and show it to your doctor at every visit. Your record lets us tell your own periods apart from unexpected bleeding, which is how we decide whether anything needs checking.

1. Reed BG, Carr BR. The Normal Menstrual Cycle and the Control of Ovulation. In: Feingold KR, et al., editors. Endotext. MDText.com; updated 2018.

2. Summary of Product Characteristics: oral micronized progesterone 100 mg capsules. Besins Healthcare (UK) Ltd; emc, UK; updated 2025.

3. Maybin JA, Critchley HOD. Menstrual physiology: implications for endometrial pathology and beyond. Hum Reprod Update. 2015;21(6):748–761.

4. The North American Menopause Society. The 2022 hormone therapy position statement of The North American Menopause Society. Menopause. 2022;29(7):767–794.

5. Reddy DS. Neurosteroids: endogenous role in the human brain and therapeutic potentials. Prog Brain Res. 2010;186:113–137.

6. Roeca C, Al-Safi Z, Santoro N. The Postmenopausal Women. In: Feingold KR, et al., editors. Endotext. MDText.com; updated 2025.

7. Panay N, Fenton A, Hamoda H, et al. Recommendations and Key Messages on Women’s Midlife Health and Menopause. International Menopause Society; 2026 (summary published in Climacteric, 2025).

8. Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence. Lancet. 2019;394:1159–1168.

9. Teede HJ, Tay CT, Laven J, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Hum Reprod. 2023;38(9):1655–1679.

10. British Menopause Society. Management of unscheduled bleeding on hormone replacement therapy (HRT). BMS Guideline. 2026.

11. Hitchcock CL, Prior JC. Oral micronized progesterone for vasomotor symptoms — a placebo-controlled randomized trial in healthy postmenopausal women. Menopause. 2012;19(8):886–893.

12. Chaikittisilpa S, Orprayoon N, Vallibhakara O, et al. Summary of the 2023 Thai Menopause Society Clinical Practice Guideline on Menopausal Hormone Therapy. J Menopausal Med. 2024;30:24–36.

13. Prior JC, Cameron A, Fung M, et al. Oral micronized progesterone for perimenopausal night sweats and hot flushes: a Phase III Canada-wide randomized placebo-controlled 4 month trial. Sci Rep. 2023;13:9082.

14. Prior JC, Cameron A, Fung M, et al. Author Correction: Oral micronized progesterone for perimenopausal night sweats and hot flushes. Sci Rep. 2024;14:17229.

15. Caufriez A, Leproult R, L’Hermite-Balériaux M, et al. Progesterone prevents sleep disturbances and modulates GH, TSH, and melatonin secretion in postmenopausal women. J Clin Endocrinol Metab. 2011;96(4):E614–E623.

16. Gordon JL, Rubinow DR, Eisenlohr-Moul TA, et al. Efficacy of transdermal estradiol and micronized progesterone in the prevention of depressive symptoms in the menopause transition: a randomized clinical trial. JAMA Psychiatry. 2018;75(2):149–157.

17. Asi N, Mohammed K, Haydour Q, et al. Progesterone vs. synthetic progestins and the risk of breast cancer: a systematic review and meta-analysis. Syst Rev. 2016;5:121.

18. Seifert-Klauss V, Prior JC. Progesterone and bone: actions promoting bone health in women. J Osteoporos. 2010;2010:845180.

19. Gleason CE, Dowling NM, Wharton W, et al. Effects of hormone therapy on cognition and mood in recently postmenopausal women: findings from the randomized, controlled KEEPS–Cognitive and Affective Study. PLoS Med. 2015.

20. Chlebowski RT, Anderson GL, Aragaki AK, et al. Association of menopausal hormone therapy with breast cancer incidence and mortality during long-term follow-up of the Women’s Health Initiative randomized clinical trials. JAMA. 2020;324(4):369–380.

21. Fournier A, Berrino F, Clavel-Chapelon F. Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study. Breast Cancer Res Treat. 2008;107(1):103–111.

22. International Agency for Research on Cancer. Global Cancer Observatory: Cancer Today (GLOBOCAN 2024). World, females, incidence by age.

23. National Cancer Institute, Thailand. Cancer in Thailand Vol. X, 2016–2018. 2021.

24. Pitakkarnkul S, Tangjitgamol S, Sangariyavanich E, et al. The situation of gynecological cancers in Thailand: incidence, histopathology, and survival outcomes from national cancer registry data. J Gynecol Oncol. 2026;37(1):e56.

25. Royal Thai College of Obstetricians and Gynaecologists. Gynecologic Cancer Screening. RTCOG Clinical Practice Guideline GY 68-038. 2025.

26. Package insert (Thailand): oral micronized progesterone 100 mg and 200 mg soft capsules. Besins Healthcare; 2013.

27. Green LJ, O’Brien PMS, Panay N, Craig M, on behalf of the Royal College of Obstetricians and Gynaecologists. Management of premenstrual syndrome (Green-top Guideline No. 48). BJOG. 2017;124:e73–e105.

28. Fournier A, Dossus L, Mesrine S, et al. Risks of endometrial cancer associated with different hormone replacement therapies in the E3N cohort, 1992–2008. Am J Epidemiol. 2014;180(5):508–517.

29. Faculty of Sexual and Reproductive Healthcare. Contraception for Women Aged Over 40 Years. 2017, amended May 2025.

30. Barretta M, Grandi G. Understanding problematic bleeding when using contraception: guidance for clinicians. Open Access J Contracept. 2025.